System for positioning heavy objects



Sept. 24, 1946. A H. HULL ErAL SYSTEM FOR PosITIoNING 4HEAVY 'OBJECTS Filed June 2o. .1942 2 shets-sneet 1 DI Il d. m Y

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THR O VLM T Sept. 24, 1946. H, 1 HULLA ET A l. 2,408,070 i SYSTEM -FOR POSITIONING HEAVY OBJECTS FiledJune 2o, 1942 2 sheets-sheet 2 INVENTORS, HARVARD L. HULL and DAVIBDYJ. MUNROE;

THEIR ATToRNE Patented Sept. 24, 1946 SYSTEM FOR POSITIONING HEAVY e OBJECTS Harvard L. Hull, East Williston, and David J. Munroe, Brooklyn, N. Y., assignors to Sperry Gyroscope Company, Inc., Brooklyn, N. Y., a corporation of New York Application June 20, 1942, Serial No. 447,828

(Cl. (iO- 53) 19 Claims.

The invention relates to systems for automatically positioning guns or other objects possessing substantial inertia in accordance with positional data supplied from a remote source and has to do with systems of the above type in which control of the positioning means is exercised by varying the setting of a speed controller.

Systems of the general type above referred to include the arrangements disclosed in the copending applications of one of the present inventors, I-I. L. Hull, joint with W. S. Gorrill and W. F. Frost, Serial Nos. 425,146 and 441,400 filed December 3l, 1941 and May l, 1942, respectively. Such systems employ both line and coarse data channels to supply control signals proportional in dilferent ratio to the errorin following, these signals being selectively utilized to control the positioning means dependent upon the magnitude of the error.

Thus, during normal operation, the ine channel signal exercises control but if the error exceeds a predetermined amount control is shifted to the coarse signal by some form of synchronizing means. Conversely if the initial error is beyond the range of control of the fine signal the coarse signal acts to reduce the error to a value within such range, after which the line signal should promptly assumecontrol. However, certain diiculties are encountered in synchronizing from a position greatly dilerent from the datum position among which is the tendency of the controlled object to overshoot not only the synchronous position but to pass through and beyond the entire range of ne control so that an oscillation or oscillators of considerable magnitude may occur before the system settles down to normal operation.

To overcome this undesirable tendency, and also to prevent undue strain of the positioning means resulting from sudden starts and stops,`

the system disclosed herein makes use of a coarse error rate term which effects retardation of the controlled object as it approaches the fine control range and thereby enables the ne signal to take control promptly when the error falls within this range. During normal operation, a ne error rate or damping term is used to prevent hunting about the synchronous position.

The effectiveness of rate terms in damping oscillations of the controlled object, and also other operational characteristics of a positional control system, is a function of the time lag or phase shift of the response of the positioning means relative to the causitive signal.v Appreciable lag occurs in many type of drives due to inertia effects, elastic deformation, and other similar factors.

Considering more particularly the driving means illustrated in the present and the above referred to applications, which has important advantages in the positioning of heavy objects, such means comprises a variable speed hydraulic gear of the type known to the trade as the Vickers gear wherein a variable displacement pump drives a hydraulic motor at a speed corresponding to the pump displacement. The operating fluid used in such a drive is usually an oil of relatively low viscosity (particularly at working temperatures) which is subjected, in operation, to pressures ranging up to several hundred pounds per square inch. Leakage in the pump and motor of such a drive increases with increasing operating pressure and may be considered to be proportional to pressure, at least to a first approximation. Likewise compression of the oil increases substantially in proportion to increasing pressure. Because of these two factors the full effect of a change of displacement setting of the pump is not at once translated into a change of operating speed of the hydraulic motor and this lag is substantially proportional to the operating pressure.

y To overcome the harmful elects of lag in the hydraulic gear on the response of the controlled object to controlling signals, including the reduced effectiveness ofthe damping signals due to improper phase relationships, the present invention includes means for obtaining and utilizing a corrective term which is proportional to the oil pressure of the hydraulic drive.

One object of the invention, therefore, is to provide in a positional control system employing iine and coarse control channels, means in addition to -normal synchronizing means, aiding the shifting of control from the coarse to the ne channel.

Another object is to provide, in a system wherein a controlled object is driven in correspondence with received positional data, means governing the operation of the controlled object driving means in accordance with ne and coarse measures of the error in following and the rate of change of each.

Another object is to provide in a positional control system employing lboth fine and coarse control channels, means for obtaining the rates of change of the error signals in each of said channels and utilizing said rates independently to damp the motion of the controlled object over different ranges of error.

Another object is to provide in a positional control system employing both ne and coarse control channels means within the coarse channel operative to retard motion of the controlled object as the ne control range is approached, thereby to prevent overshooting said range.

Another object is to provide, in a control system employing hydraulic driving means, compensation for factors delaying or modifying the out- 3 put response of such means to an input impulse or signal.

Another object is to provide compensation for the compressibility of the operating fluid in hyfdraulic driving means for a controlled object in a positional control system.

Another object is to provide compensation for phase displacement in such' hydraulic means between an applied controlling impulse and theresponse of the driven object thereto. Y

A further object is to compensate for variable leakage in such hydraulic means. v

Other objects and advantages of this invention will become apparent as the description proceeds.

It is to be understood that the term factor as employed herein and in the claims is to be construed as including not only those factors hereinabove stated for exemplary purposes as inertia, elasticity, leakage and compression, such examples being applicable to the hydraulic systern herein illustrated, but also as including other factors which are detectable or measurable and which cause lag in the system. Additionally, elastic deformation of an element, as recited in the claims, may occur in a hydraulic sense in the lluid, as an element, as well as in a mechanical sense in various parts or elements of the drive.

In the drawings,

Fig. 1 is a schematic representation of a system, according to the invention, for positioning a gun or other heavy controlled object in accordance with received positional data.

Fig. 2 is a detail, partly in section, of a pressure sensitive device suitable for obtaining an electrical signal.

Fig. 3 is a sectional view of a different type of pressure sensitive device.

Fig. V4 is a diagram of an electrical circuit suitable for use with the device of Fig. 3.

Referring now to Fig. 1, the apparatus units shown Within the dashed lines in the upper lefthand corner are normal elements of a gunfire director, for example, of the type described in U. S. Patent No. 2,065,303, to E. W. Chafee et al., dated December 22, 1936. These units together with the other apparatus of Fig. 1 constitute control means for aiming the gun in one dimension only, e. g., in azimuth. It is to be understood that,'in addition, a similar grouping'of apparatus, omitted here to simplify the illustration of the invention, will, in practice, be used to govern the aiming of the gun in elevation. Also, certain auxiliary apparatus such as power limiting means, manual operating means and hydraulic limit stops, disclosed in the aforementioned applications 425,146 and 441,400, may advantageously be employed in connection with the arrangements of the present invention, reference being had to the prior applications for details of such devices.

The value of gun azimuth angle as computed by 'the director is represented yby the angular position of shaft il). Since the shaft I!) corresponds to the computed gun position data it rep-y resents corresponding positional data. It will be appreciatedy however, that instead of being an element of a nre control director, shaft I@ may itself be considered either a controlling object or a source o f positional data. On the other hand it may be connected to and angularly positioned by any other controlling object, for example, a telescope or other sighting device. Shaft I drives the rotors of'neand coarse Selsyn transmitters I2 and I4 at `different rates determined by the ratio of gears I I. Both transmitters have stator windings excited from a single source of alternating current 5 which is preferably a comf mon supply for the entire system in order to fsecure a uniform phase. Fine transmitter I2, which is driven at the faster rate and therefore vgenerates the larger of the two signals for a given displacement of shaft ID, has its rotor winding connected by three-conductor transmission line I5 to the winding of stator I6 of Selsyn receiver -I1 Which is operated as a synchro transformer o-r signal generator by having its rotor I8 driven from gun 2D by Way of shaft 2l and intermediate gearing 22. Y Y

Rotor winding of coarse transmitter Irl is connected by three conductor transmission line 26 to a pair of Selsyn receivers, one of said receivers 21, being operated as a free rotor device. Receiver 21 has a rotor 29 carrying on its shaft a, contact 30 which may be closed, upon suitable displacement of rotor 29 in one direction or the other, to either of contacts 32 or 33, theseftwo contacts being connected in parallel. Receiver 21 has a casing, not shown, of a known type mounted for rotation and geared to the gun so that the entire receiver turns with the gun while the rotor 29 thereof is free to turn with respect to the casing. This arrangement is shown in the patent to Mittag et al., No. 1,958,245, issued May 8, 1934. The second receiver 35 is likewise connected to transmission line 26 and is operated as a ysynchro transformer by having its rotor 3l driven from gun 20 by-way of shaft 38 and intermediate gearing 39 to furnish a coarse positional control signal.

The utilized ne error signal is derived from the alternating potential induced in winding i8 by applying this potential to potential divider resistance 4I) having an adjustable contact 4 I. The rate of change of the ne error is obtained by applying the voltage of winding I8 to a balanced modulator or full-wave rectier comprising a pair of `bridge type rectiers and 46 which may each f comprise elements of the dry `disc type. In order to obtain a phase sensitive device, each half wave rectifier is supplied with an A. C. bias from the common supply, rectier 45 being biased by a,

voltage supplied -by way of transformer 41 and rectiiier 4E by a voltage from transformer 48.

The joint output of rectiiers 55 and 4B, which is a reversible polarity continuous voltage, is filtered by means such as low pass lter to remove ripple and applied to an electrical diifer- 55 entiating circuit comprising condenser 55 and ,resistance 51 connected in series.

lt is known that in order to effect differentiation, the time constant of such a resistance-capacity network should be low or, if alternating quantities are considered, the reactance of condenser 56 should be large in comparison with the value of resistance 51 and under such conditions the voltage across resistance 51 may be considered to be substantially proportional to the.

time rate of change of the output of lter 55,. i. e., proportional tothe rate 0fA change of the fine error signal. The voltage across resistance 51 is applied, together with the fine error voltage taken from resistance 40, as an input to ampliiier 60 in combination with certain other signal volt-v ages to be described hereinafter.

The coarse error signal is derived from the alternating potential in winding 31 by Way of input transformer 15l and is rectied in abal- 75. anced phase-sensitive` modulator or rectifier 18 5 comprising bridge-type rectiers 79 and 80, respectively biased from the common A. C. supply by voltages introduced through transformers 82 and 83 respectively. The output of rectifier 'i8 is iiltered in low pass filter 85 to remove ripple and the D. C. component is applied to a difierentiating circuit comprising condenser 8l and resistance 88 in series. Condenser 81 is shunted or by-passed by a resistance 90. The utilized signal is the voltage acro-ss resistance 88 which is applied in series with the previously described signals and other signals to be described hereinafter as an input to amplifier 6U.

Amplifier E may be of the type described in applications 425,146 and 441,400 previously referred to, comprising a modulator stage including tube IGI Which receives an alternating voltage both as a plate supply and as a grid bias. Tube iol is coupled to a second amplifying stage including tube IM, the output of which, through transformer |05, is applied to one of the stator phases |96 of two-phase induction motor |01 having a second phase Hi8 supplied from the common A. C. source through a phase-adjusting condenser Ili. A distinctive feature of ampliiier til is that it supplies a reversible phase A. C. output responsive to either a reversible phase A. C. input or a reversible polarity D. C. input or the two in combination. This makes it unnecessary to convert all of the control signals to one type of electrical quantity, alternating or continuous potentials being equally eifective in controlling the ampliiier output.

Motor IS? drives shaft I IB on which is mounted crank H2 operatively connected to reciprocate stroke rod I I4 of the variable displacement pump or A end IIS of a Vickers variable speed hydraulic drive, generally designated by reference numeral |2ii. Pump IIS is continuously driven by motor I and its displacement may be varied by changing the angle between the drive shaft of the pump and the drive shaft of motor IIS,

which angle is, in turn, determined by the longitudinal position of stroke rod IIE. A universal driving connection (not shown) permits tilting of the entire pump relative to the motor shaft under the control of the stroke rod. Pump IIS supplies operating iiuid at a rate dependent upon its eiiective displacement to the hydraulic motor or B end or" the Vickers drive H9, by Way of connecting pipes H5 and III, to operate this motor at a speed substantially proportional tc the displacement of the pump and therefore proportional to the position of stroke rod I |12. Motor H9, through gearing |22, drives platform |213 on which gun 2i) is mounted.

A direct current generator |25 of either the permanent magnet type or having a suitably eX- cited iield is driven by stroke motor |53? at a speed proportioned to the rate of change of position of stroke rod IIll. The actual operating speed of generator |25 may be determined by gearing or other connecting means, as III, between shaft IIB and the generator armature shaft. The continuo-us potential output of generator |25 is applied to an integrating and combining circuit |725 comprising an input potential dividing resistance |23 having an adjustable contact |29 slidable thereupon and resistances li and $32 and condenser ISS connected in series. Resistance |36 is preferably adjustable. The output of integrating circuit |26 is the voltage drop across condenser |33 and across a portion of resistance |32 determined by the setting of `adjustable contact |35 thereupon. This output voltage is applied 6 as an input to amplifier B by way of the series' circuit combining the several control signals.

As previously stated, the effect of damping signals is reduced by the lag or phase displacement in the response of the hydraulic motor to adjustment of stroke rod IIA, due to leakage and compression of the hydraulic pressure fluid. In order to compensate for this lag or phase displacement, a signal corresponding to changes in the pressure of fluid, i. e., changes in the torque of the motor, is developed and used to modify the control signals in the following manner.

The pressure at which operating fluid is supplied by pump I6 to motor l I9 governs the actuation of a further signal generating device Ill@ shown more in detail in Fig. 2. In this iigure it will be seen that the pressures existing in pipes Ill and IIE are communicated to a pair of opposed pistons lill and |52, respectively. by 'way of connecting pipes U33 and isili, respectively. Piston lill i5 displaceable in cylinder |45 by oil pressure in pipe M3 against the opposition of spring It while piston |42 is displaceable in cylinder 68 by pressure in pipe IM against the opposition of spring Md. Pistons lili and M2 are mounted on opposite ends of a common piston rod |59, which, through4 a pin and slot connection I rotates rocker arm |53 about pivot point Id. Through another pin and slot connection |55 at its lower end rotation of rocker arm 53 is caused to translate cylinder block |57, slidable in guides |59 and |65.

Cylinder block I 5l' has a cylindrical bore it in which pistons |62 and |83 slide. These pistons are mounted `on opposite ends of piston rod I/l which has a central lateral extension or arm |65 carrying at its extremity the magnetically permeable armature |57 of a pick-oif device |58 which includes a magnetizable core I'Ill cooperating with armature IE?. Resistance to displaca ment of the assembly of piston rod i 5d and armature |55 is provided by oppositely acting springs H2 and |72' which centralize armature IGT relative to core im. The opposite ends of bore lii in cylinder block |57 are connected by a restricted conduit H5 and this conduit and the end portions of the bore are preferably iilled with a viscous fluid which is pumped through the conduit upon displacement of the pistons. Suitable means for replenishing fluid lost by leakage pa'st the pistons may be provided. Conduit H5 is adjustably restricted by means of screw operated needle valve lll to provide variable opposition to the transfer of fluid between opposite ends of cylinder IBB and thereby a variable time delay in the centralizing of armature |67.

Core Ill? of pick-off |63 is formed with three parallel legs, the central leg being provided with an exciting winding H9 connected to a suitable A. C. source, while the outer legs mount, respectively, the coils of output Winding E35, connected by leads |22, |82 t0 the input circuit oi ampliiier t0. Pick-Gif its is of a well known type which is Widely used as a signal pick-off from sensitive instruments for translating displacement of a member into an alternating electrical potential. Thus, when armature |51 is centraiized with respect to core Ilil, the two Iparts of winding |86) receive equal alternating potentials by induction which may be caused to annui one another. When armature i6? is displaced, however, this balance is upset and a net alternating voltage proportional to the displacement exists in winding |80. 5

As alternative means for obtaining any electrical output responsive to the operating pressure of the variable speed hydraulic drive, there is shown in Fig, 3 a pair of carbon pile devices |83, |84 which are adapted to be actuated in accordance with the pressures in pipes l| and ||1. Pistons |85 and' |86 of these devices are slidable in cylinders |81 and |88 respectively. Piston |85 is integral with a pressure plate |90 which bears on a stack of carbon discs ISI in an insulating housing |93. Electrical contact to one end of the stack is made by way of plate |90, piston |85, cylinder |81 and output connector ld while connection to the other end of the stack is made by Way of conducting plate |95 and output connector |96. Similar arrangements in device |84 permit 4change of pressure exerted on piston |86 to cause variations of the resistance of carbon pile |92 which may be connected in circuit by leads |93 and |98.

The carbon piles |9| and |92 of devices |83 and |84 respectively form variable resistances which may be utilized as elements in a variety of circuits, one of which is shown in Fig. 4. In this circuit, fired resistances 2Q!) and 25| form with variable resistances |9| and |92 a Wheatstone bridge circuit excited by battery 263 and supplying an output potential to a circuit comprising condensers 255 and 206 and resistance 291 in series. Condenser 2535 may be shunted by a resistance 268 to obtain an output. The potential drop across resistance 231 may be applied by way of leads |82 and |82 to the input to ampliler 66 as a substitute for the potential applied by this lead in Fig. 2.

In order to trace the operation of the described system, assume that shaft lll experiences a more or less sudden angular displacement proportional to a change of computed gun azimuth angle. An alternating potential proportional to this displacement is induced in winding lil and a fraction thereof, determined by the setting of contact lil, is taken from potential dividing resistance as the utilized ne error signal. At the same time, there is obtained at the output of filter 55 a continuous Voltage likewise proportional to the voltage in winding I8 and, through the operation of the differentiating circuit vcomprising condenser 56 and resistance 51, there is obtained across resistance 51 a continuous potential proportional to the rate of change of the iine error signal.

Under the influence of the fine signal and the rate of change thereof, motor |51 is caused to position pump stroke rod I4 of the Vickers drive to change the operating speed of hydraulic motor |Q of said drive. Owing to the resulting change of displacement of pump ||5 while this pump is being operated at a constant speed by motor i8, a change of operating pressure occurs in connecting pipes H5 and lil which is transmitted to pistons lill and M2 (Fig. 2) and causes a displacement of piston rod |50 from its central position which, through connecting linkage, causes a translational displacement of cylinder block |51.

Pistons |62 and |33 in cylinder |50 Will initially follow the motion of cylinder block |51 against the differential opposition of springs |12 and |12' thereby displacing armature |61 and inducing an unbalanced alternating potential in two-part output winding |88 on core |10. This potential is applied by leads |82 and |82' to the control circuit which combines the various input signals applied to amplier 6G. After the initial displacement of armature |51, a. gradual centralization occurs under the influence of springs |12, |12 which is permitted by pumping. of uid through 8 conduit |15 from one end of cylinder |60 to the other at a rate determined by the adjustment of needle valve |11. Thus, during extended periods when a constant pressure diierence exists between pipes l l 5 andl |1, no net signal is supplied by device |68.

The damping of the system, as in the arrangement of the above-mentioned application Serial No. 441,400, is obtained by causing the output of direct current generator |25 (operated in correspondence with change of position of stroke rod Hd) to be applied to integrating and combining circuit |25 which supplies as an output a continuous potential having components proportional to the input voltage to circuit |26 and to the time integral of said voltage, that is, respectively proportional to the rate of change of position of stroke rod iid and to the position of said rod, the latter component therefore being substantially proportional to the rate of change Of displacement of gun 25.

The first named component, which is the drop across a portion of resistance |32 determined by the position of adjustable contact i355, is by its nature effective in damping oscillations of stroke rod ill and associated members, while the second component is effective in damping oscillations of the gun. The time constant of the integrating circuit comprising resistances |3il and |32 and condenser |33 is adjustable by Varying the Value of resistance |353.

The coarse error signal is obtained in a manner similar to that described in connection with the fine error signal. Displacement of shaft Ill causes a Voltage proportional thereto to be induced in winding 31 of the coarse synchro transformer or signal generator of a phase corresponding to the sense or direction of the displacement. The output of filter supplies a continuous potential proportional to the alternating voltage of Winding 31 and the potential drop across resistance 88 has components respectively proportional to the applied voltage and the rate of change thereof, the first component being derived by way of the path which includes resistance 9U and the second of the components being derived by Way of the path which includes condenser S1. These two components are, respectively, the coarse error signal and the rate of change of signal which are applied to amplier 6|).

During normal operation, the coarse error signal is of negligible importance in comparison with the fine error signal but when a predetermined magnitude of error is exceeded, contact 39 operated by coarse Selsyn receiver 21 is closed to either of contacts 32 or 3?, depending upon the sense of the error, thus short-circuiting the outputs of the fine error and fine error rate circuits, control then being exercised by a combination of the coarse error, coarse error rate, the damping signals and the hydraulic pressure signals. In synchronizing the sending and receiving elements of the system, when the value of the error causes the coarse channel to be in control, the control term proportional to the rate of change of the coarse error opposes the effect of the error signal in proportion to the rate of change thereof and thereby slows the speed of operation of motor m1 and may reverse the direction of operation thereof before the synchronizing point is reached, thereby slowing hydraulic motor 5 to prevent passing through and over-shooting the ne range of control.

As soon as the error is within the iine control range, Contact 3|] is disengaged from Contact 32 or 33, as the case may be, and the fine error signal and its rate immediately become eiective in bringing the gun to the exact synchronizing point. To summarize the effects of the various control signals which are utilized, normal control is exercised by the line error signal and fine error rate, the latter term tending to prevent hunting within the fine range of control. The damping signals obtained from circuit H26 are effective in stabilizing the system and preventing hunting of the members thereof and the occurrence of a constant speed lag is prevented since the charge on condenser |33 leaks ofi during extended intervals of constant speed operation and no output is then obtained from circuit |25. The occurrence of speed lag in a system in which the driving means is velocity controlled, such as is described herein, is further discussed in application Serial No. 441,400.

'Ihe signal obtained in response to change of oil pressure of the variable speed hydraulic drive, by increasing the output of amplier ll when there is a sudden increase in oil pressure in correspondence with a demand for a sudden change of operating speed of motor H9, dies away when this pressure remains constant and therefore is inoperative to change the positional phase at which gun 2li follows a constant rate of change of data.

Since amplifier 60 is responsive to both alternating and continuous potentials, the modification of the oil pressure signal generator shown in Fig. 3, which as used in the circuit of Fig. 4 furnishes a continuous potential output across resistance 287, is adapted to provide a signal compensating for lag in the hydraulic transmission arising from oil compression and oil leakage, particularly during periods of suddenly increased pressure, in a manner generally similar to the use of the alternating output 'of device Hi8. It will be apparent that differential compression of carbon piles I9! and E92, by bringing about a change of the balance of the bridge circuit, causes a continuous potential to be applied across condensers 2115 and 2535 and resistance 2M. By shunting condenser 205 with resistance 208' the voltage across resistance 201 may be caused to have a component proportional to the supply voltage while the effect of condenser 28E is to produce a component substantially proportional to the rate of change of the applied voltage. Condenser 205 acts mainly as a blocking condenser so that when the charge on condenser 266 leaks off during periods of constant diierential oil pressure no voltage appears across resistance 20? and the oil pressure term disappears.

As many changes could be made in the above construction and many apparently widely diiferent embodiments of this invention could be made without departing from the scope thereof, it is intended thai all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described our invention, what we claim and desire to secure by Letters Patent is:

l. In a positional control system, a controlled object. driving means therefor, a source of positional data, means for obtaining line and coarse measures of the disagreement between the position of said object and data of said source and a measure of the rate of change of said disagreement, coarse synchronizing means operative to control said driving means in accordance with a combination of said coarse measure and said rate of change of. disagreement during the occurrence of disagreement of large magnitude, means operative to control said driving means in accordance with said iine measure during the occurrence of disagreement of lesser magnitude, and means shifting control between said last two means at a predeterminedvalue of disagreement.

2. In a positional control system, a controlled object, driving means therefor, a source of variable positional data, means exercising normal control of said driving means responsive to disagreement between the position of said object and data of said source within a portion of the range of said data, including means for suppressing hunting during normal control, and means operative during the occurrence of disagreement greater than said portion of the range of said data to control said driving means in accordance with a combination of quantities including the rate of change of disagreement, to return said object to the range of normal control without oscillation.

3. In a positional control system, a controlled object, driving means therefor, a source of positional data, coarse and fine control channels for said driving means each including means for generating a signal proportional to disagreement between the position of said controlled object and the data of said source and for obtaining therefrom the rate of change of said signal, said two signals being proportional in different ratio to the disagreement, and means for shifting control from one of said channels to the other at a critical value of disagreement.

4. In a positional control system, a controlled object, driving means therefor, a control for said driving means, a source of positional data, means for obtaining a signal proportional to the rate of change of disagreement between the position of said object and the data of said source and for applying said signal to said control to damp `the motion of the con-trolled object, and means for obtaining and applying to said control a signal measuring change of a. factor tending to cause a phase displacement between said first signal and the response oi said object thereto, .thereby to maintain said response in proper phase relationship to effec-t said damping.'

5. In a positional control system, a. controlled object, driving means therefor, a source of positional data, means for obtaining ne and coarse signals proportional in different ratio to disagreement between the position of said object and the data of said source, means for obtaining a signal proportional to the rate of change of disagreement, selective means for controlling said driving means in accordance with said iine signal during the occurrence of disagreements of limited magnitude and in accordance with a combination of said coarse signal and said rate of change signal during the occurrence of disagreements of greater magnitude, and means further controlling said driving means in accordance with the magnitude of a factor tending to cause a phase displacement between at least one of said signals and the response of said object thereto.

5. In a positional control system, a controlled object, driving means therefor, a controlling object, means furnishing signals corresponding .to the positional disagreement of said two objects and controlling said driving means in accordance therewith, and means furnishing a measure of a factor causing a lag in the response of said driving means to said signals for further controlling said driving means in accordance therewith to compensate for said lag.

7. In a positional control system, a controlled object, driving means therefor, a controlling object, means furnishing a measure of the positional disagreement of said two objects and controlling said driving means in accordance therewith, and means responsive to elastic deformation of an element of said driving means for further controlling said driving means to compensate for a phase shift introduced by said deformation between an input to and an output from said driving means.

8. In a positional control system a controlled object, driving means therefor including a hydraulic transmission, a controlling object, means for controlling said driving means in accordance with the positional disagreement between said two objects and means responsive to changes of pressure of the operating uid in said hydraulic transmission for modifying the control of the control means to compensate for lag in the hydraulic transmission arising from compression and leakage of the operating fluid.

9. In a control system, a controlled object, a hydraulic drive therefor, a displaceable controller, means governing the operating speed of said drive in accordance with the positional disagreement of said object and controller, and means responsive-to change of pressure of the operating fluid of said drive for controlling the governing means to alter the speed of said drive to compensate for lag therein, said speed alteration disappearing during extended periods of constant pressure.

l0. In a control system, a controlled object, a displaceable controller therefor, means causing said object to follow displacement of said controller including a hydraulic driving element and an element hydraulically driven therefrom, and means responsive to changes of pressure of the operating fluid of said hydraulic elements for altering the speed of said driving element yto com pensate for lag arising from compression and leakage of the operating fluid.

ll. In a positional control system, controlling and controlled objects, means effective on the relative displacements of the objects for fun nishing a measure of the positional diagreement thereof, variable speed hydraulic means operan ed by the controlling object for driving the con trolled object into positional agreement with the controlling object, means furnishing an impuise of adjustable duration upon change of pressure of the operating fluid of said hydraulic means, and means jointly controlled by the rst and last mentioned means for controlling the speed of said hydraulic means in accordance with a combination of said measured quantity and said impulse.

l2. The combination as claimed in claim ll in which the means furnishing an impulse of adjustable duration comprises a pressure actuated, variable inductance device, means biasing said device to a neutral condition and a time delay device for retarding the operation of said biasing means.

13. In a positional control system, controlling and controlled objects, variable speed driving means for driving the controlled object comprising a variable displacement pump, a hydraulic motor and a pair of conduits connecting said pump and motor to secure a continuous ilow of operating iiuid therebetween, and means for controlling the displacement of said pump respo-nsive respectively to positional disagreement of said two objects and to change of the differ ential pressure of lthe fluid in said two conduits.

14. In a positional control system comprising controlling and controlled objects and servo means causing the controlled object to move in correspondence with the controlling object including a variable speed hydraulic transmission. means Vfor compensating for variable transit .time of impulses through 'said transmission. including means supplying a controlling impulse to said hydraulic transmission having components respectively proportional to changes of pressure of the operating fluid and the rate of said changes.

l5. In a positional control system, a controlled 'object variable speed hydraulic driving means therefor, a controlling object, means controlling the speed of said driving means in accordance with the positional disagreement of said two objects, and means for adjusting said speed rcsponsive to change of pressure of the operating fluid of said driving means, including means for gradually cancelling said adjustment during periods of constant pressure operation.

i6. The combination as claimed in claim l5 in which adjusting means includes a two part inductive pick-ofi", means actuated by differential pressure changes in the operating fluid of said hydraulic means for relatively displacing the parts of said pick-oil, spring centralizing means for returning said pick-ori to neutral condition and adjustable delay means retarding the operation of said centralzing means.

i7. The combination as Vclaimed. in claim l5 in 'which said adjusting means includes a pair oi resistance elements connected in a bridge circuit, means for differentially varying the resistance ci' said elements responsive to pressure changes in the operating fluid of said hydraulic means and a condenser-resistance network of predetermined time constant in the output of said bridge circuit for obtaining a transient potential responsive to bridge imbalance.

18. A device for obtaining a transient eiectrical impulse in response to a change of pressure comH prising a pair of members coupled by viscous drag means, means responsive to change or" pressure for displacing one or" said members, a two part piek-off generating an electrical potential re sponsive to relative displacement of the parts thereof from a neutral position, means biasing said parts toward said neutral position, means operatively connecting one part or said pick-oil' with the other of said coupled member-s and means for adjusting the viscous coupling between said coupled members.

19. In a positional control system, a controlled object, variable speed hydraulic driving means therefor, a source of positional data, means for controlling the speed of said driving means in accordance with data supplied by said source, means for transiently controlling said hydraulic driving means in accordance with changes in the operating speed thereof to damp motion of the controlled object, and pressureresponsive means effective on .the initial operation of the hydraulic driving means for further ran'siently ccntroliing the speed of said hydraulic driving means in ac cordance with change of pressure of the operating iluid oi' said hydraulic driving means.

HARVARD L. l-IUL DAVID J. MUNROE. 

